1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device and a method for operating the same, and more particularly, to a nonvolatile memory device performing an erase operation and a method for operating the same.
2. Description of the Related Art
A nonvolatile memory device refers to a memory device which maintains data stored therein even though power supply is cut off. Currently, a variety of nonvolatile memory devices, for example, a NAND-type flash memory and so on are widely used.
The nonvolatile memory device having a plurality of memory cells may perform a program operation to write data in memory cells, an erase operation to erase data written in memory cells, and a read operation to read data written in memory cells.
Here, the erase operation of the nonvolatile memory device is performed per memory block of memory cells. This may be more specifically described as follows.
When an erase operation begins, a ground voltage 0V is applied to word lines of a selected memory block, while word lines of an unselected memory block stay in a floating state after the ground voltage 0V is applied. In such a state, when a high voltage called an erase voltage is applied to a substrate, data of memory cells belonging to the selected memory block are erased by a voltage difference between the word lines and the substrate, i.e., a difference between the ground voltage applied to the word lines and the erase voltage applied to the substrate. On the other hand, since the word lines of the unselected memory block stay in a floating state, the voltages of the word lines are boosted when the erase voltage is applied to the substrate. Accordingly, a voltage difference between the word lines and the substrate disappears in the unselected memory block. Therefore, the data of the memory cells belonging to the unselected memory block are suppressed/prevented from being erased.
During such an erase operation, however, although the data erase of the memory cells in the unselected memory block is to be suppressed, data of partial memory cells may be substantially erased. That is, a so-called erase disturbing may occur. This is because the voltages of the floating word lines of the unselected memory block are not adequately boosted but lowered to a certain level or less.
When such an erase disturbing occurs, the reliability of the nonvolatile memory device may be reduced, and malfunction may occur.